Determination of binding constants of hydrophobically end-capped poly(ethylene glycol)s with β-cyclodextrin by affinity capillary electrophoresis

The formation of inclusion complexes between methoxypoly(ethylene glycol)s (MPEG)s bearing one hydrophobic group (phenyladamantyl) per chain and β-cyclodextrin (β-CD) was studied by capillary electrophoresis (CE). The effect of highly sulphated β-CD (HS-β-CD) on the migration behaviour of the phenyladamantyl-modified MPEG (MPEG-PhAd) analyte was investigated. It was established that the interaction between the modified PEG and β-CD involved a 1:1 stoichiometry. Non-linear regression and three usual linearization methods (y-reciprocal, x-reciprocal and double reciprocal) were employed to estimate the binding constants. It was demonstrated that the binding constants were similar (around 400 M−1) for two MPEG-PhAd having different chain lengths (2000 and 5000 g/mol).